I don't know if people are still using old flash versions but rigging is way more manageable if you can parent your layers and automate elbows/knees, you can do this in Adobe Animate; In After effects there's a plugin dedicated to just that, I'd recommend this rigging tutorial so you can see how it works. https://www.youtube.com/watch?v=i63vPXJ00r0 even if it's not sprite animation it's still 2D character animation